It wasn’t until she became a young woman that Kristen Schaal realized she still sounded like a little girl. “In college they were like, ‘You talk funny.’ In my head I sound lofty and deep and just beautiful, so I was shocked,” says the actress and comedian.

Since then she has turned that quirk into a powerful comedic asset. As a breathy coo, a glottal gurgle or a menacing shriek, the voice has accentuated her doll-like features in roles such as the groupie Mel in “Flight of the Conchords.” She’s been a supporting player in movies like “The Muppets” and “Dinner for Schmucks,” and she’s now a recurring guest star on “30 Rock,” playing Hazel Whassername, an NBC page with a “demonic layer.” (She doesn’t know how long her run will continue, but “30 Rock” producers have asked her to keep some shooting dates open in April, she says.)

Schaal does have a leading role, by way of her voice, on the animated TV series “Bob’s Burgers,” which returns on Sunday for a second season on Fox. She plays Louise, the youngest child of the show’s plucky nuclear family. Series creator Loren Bouchard describes Louise, who is never seen without her pink bunny ear hat, as a “maniacal” kid who takes pleasure in “sh– stirring mischief.” In one episode she instructs her dweeby older brother Gene (Eugene Mirman) how to cheat in a mascot race during a local baseball game—with a knife doused with lemon juice strapped to his foot. “Stab stab stab! Sting sting sting! Sweet baby blade foot!” Louise crows.

Schaal remembers herself as a well-behaved youngster who was terrified of authority, but says with Louise she’s channeling some kind of small, inner animal. “It’s just me doing me, but me doing a nine year old who I’d never want to meet, or baby sit, or have in my family, any of it.”

It was only after Louise’s character took shape that the show’s writers realized her similarities to another diabolical young cartoon character, Stewie Griffin of “Family Guy” fame. “He casts a large shadow,” Bouchard says. But he points out that Stewie’s default expression is menacing, with eyebrows pointing down; Louise is drawn with eyebrows arching up over her round eyes, giving her a look of just-foolin’-around innocence. Bouchard adds, “Kristen is very protective of her. If Louise is getting too bratty she lets us know about it.”

In an coming episode, Louise gets her bunny ears stolen by a bully, prompting a full-blown rampage. But fans shouldn’t expect a complete explanation of why she wears the hat in the first place, Schaal says: “That’s the mythology of the show. You can’t really give that away, in the same way you’ll never hear Maggie [Simpson] speak. Maybe in the 27th season.”